Phosphor materials are well known for various uses. One such use is as X-ray storage phosphors. An X-ray storage phosphor exhibits photostimulated luminescence after exposure to an X-ray dose of radiation and subsequent exposure to an excitation source, such as a light source (e.g., visible light, infrared). Thus, the phosphor has the ability to store some of the X-rays it is initially dosed with so that it can emit that energy later. The secondary excitation needed to cause the emission of radiation in storage phosphors is commonly referred to as stimulation radiation. Storage phosphors are used in imaging plates to acquire images in a digital format and to produce images that may be electronically displayed on a screen or printed. The storage phosphor is typically incorporated into a binder in the imaging plates, with the binder applied to a suitable support. There are several known methods for recording and reproducing an X-ray pattern using X-ray storage phosphors. See, e.g., U.S. Pat. Nos. 5,514,298 and 4,258,264, each of which is incorporated in their entirety herein by reference.
It would be desirable to identify useful storage phosphors having relatively high densities. Theoretically, phosphors having high densities are capable of producing a useful phosphor layer that is thinner than is currently in use. Higher density phosphors provide relatively high absorption of penetrating radiation, which potentially results in higher image resolution. One prototypical X-ray storage phosphor, BaFBr:Eu, has the relatively low density of about 4.96 g/cc.
Phosphors commonly comprise a host compound that may be doped with an activator element. For example, U.S. Pat. No. 5,391,884 discloses a gadolinate host activated with either terbium or terbium and samarium. Other gadolinium-hosted phosphors are known, see, e.g., U.S. Pat. Nos. 4,959,174, 4,829,188 and 4,857,741. Certain compositions are known as direct conversion x-ray phosphors, but not as storage phosphors. See U.S. Pat. No. 4,822,696.
There continues to be a need for materials that are suitable storage phosphors, particularly those having higher densities.